1. Field of the Invention
The present invention relates to a method and apparatus for testing a solder material for deterioration degree.
2. Description of the Related Art
On the production line of printed boards, electronic components are mounted onto the board by performing a printing process to print a solder material to a board, a mounting process to mount an electronic component onto the printed solder material and a reflow process to fix the electronic component on the board by soldering.
In the printing process, the solder material is put on the surface of a metal mask placed on the board. The metal mask is formed with an opening corresponding to a wiring pattern. The solder material on the metal mask surface is pushed and rotationally moved by a movable squeegee. Furthermore, the solder material being rotationally moved is squeezed out of the opening onto the board by the urging force of the movable squeegee. Based on this process, the solder material is printed to the board (see paragraph [0011] in JP-A-5-99831).
The metal mask is in continuous use for a number of boards, in a state where the same solder material is rested thereon. Accordingly, the solder material is rotationally moved by the movable squeegee repeatedly each time printing is performed. The solder material gradually deteriorates due to rotational movement, and the deteriorated solder material constitutes a factor causing defects on the printed board.
For this reason, when the solder material on the metal mask is analyzed in-line for deterioration degree and the solder material is deteriorated significantly, it is quite important to replace the solder material lying on the metal mask. In addition, before supplying a solder material onto the metal mask, it is important to analyze the deterioration degree of the solder material to supply and check whether or not there is a deterioration in the solder material before it is supplied.
Here, the solder material has a viscosity, oxidation degree and reducing power that serves as an index in evaluating the deterioration degree thereof. The reason the viscosity, oxidation degree and reducing power is used as an index is because of the following.
It is known that, as solder material deteriorates, its viscosity increases to proceed oxidation and lower the reducing power. Herein, it is also known that, when a highly viscous solder material is printed on the board, defects such as “breakages” or “blurs” readily occur on the board thus printed. Meanwhile, it is also known that, in case an oxidized solder material is printed to the board, inferiorities such as “solder balls” or “solder unfused” readily occur on the post-reflow board. Furthermore, it is also known that, when solder material which is lowered in reducing power is printed to a board, such an inferiority as “wettability reduction” readily occurs on the post-reflow board.
Namely, the viscosity, oxidation degree and reducing power of a solder material is correlated to the occurrence rate of printed board inferiorities. For this reason, the viscosity, oxidation degree and reducing power of a solder material serves as a significant index in evaluating the deterioration degree of a solder material.
Conventionally, there are various methods to analyze the deterioration degree of solder material, as exemplified in JP-A-5-99831 (date opened: Apr. 23, 1993), JP-B-8-20434 (date published: Mar. 4, 1996) and JP-A-10-82737 (date opened: Mar. 31, 1998).
JP-A-5-99831 discloses a method to measure the viscosity of a solder material depending upon a velocity of a solder material flowing on a squeegee surface. However, this method can measure the viscosity of a solder material only when driving the squeegee. Thus, there is a problem that the test sample is limited to a solder material being used in a printing process.
Consequently, JP-B-8-20434 discloses a method to measure the acid degree of a solder material (flux) by conducting a titration by use of a solder material sampled. However, in this method, there encounters a problem that labor and time is required in conditioning a reagent.
Meanwhile, JP-A-10-82737 discloses a technique to measure the surface oxidation rate of a solder material according to ultraviolet-ray photoelectron spectroscopy. However, this method uses ultraviolet radiation that is harmful to the human body, and hence is not preferred in view of operation hygiene.